Transparent glass plate



Patented July 22, 1930 UNITED sT Es PATENT OFFICE HENRY B. HIGGINS, or PITTSBURGH,- PENNSYLVANIA, assxenon TO PITTSBURGH PLATEVGLASS COMPANY, A CORPORATION or PENNSYLVANIA TnANsraRENremss PLATE R Drawing.

a much less cost. Heretofore two.varieties of glass have been employed for the purposes above set forth, one being what is known as window glass, or sheet glass, and the other what is known as plate glass. v

Window glass is produced by a drawing, operation, either in the form of cylinders which are flattened and cut up, or in the form of a continuous sheet by the well known Colburn (U. S. Patent No. 1,248,809) and Fourcault (U. S. PatentNo. 901,800) proc' esses. This form of glass has a natural fire finish or polish, so that it requiresno me-' chanical surfacing, andv for this reason is relatively cheap. It has the disadvantage, however, that the surfaces although highly polished are not optically true, so that the surface presents a wavy appearancewith reflected light when viewed at an angle, and

' also has the further objection, when used in glazing, that thereis a distortion-in the appearance of objects viewed through it at an angle.

Plate glass is produced by a casting or arolling operation, so'that the surfaces are roughened or marred and require grinding and polishing. The rough glass is ground 15 till it is flat and true upon rotating tables over which grinding runners are mounted, abradants comprising sand and-emery being successively employed for this purpose. The glass which is thus'given a perfectly flat true 40 surface, is then polished upon the same rotating table by the use of runners faced with felt to which rouge is supplied. This givesthe glass a brilliant luster. The surfaces thus produced not only have the luster of the fire finished window glass, but inaddition are optically true. That is, the face of the sheet when viewed at an angle shows a perfectly plane uniformsurfacewithout waves, and when objects are viewed through the glass at an angle, there is no distortion. Plate glass,

Application filed 4 m 21,

:ing and polishing,

1925. Serial No. 24,856.

window glass and is required wherever trueness of vision'is a controlling factor. Its

cost per foot,, however,' is many times that of window glass, ,dueto the expense of grindso thatits field of use is greatly restricted. a

' It is the purpose of the present invention to provide glass sheets, which in cost lie between that of window, glass and plate glass and which have manyof the advantages incident to plate glass, rendering the glass greatly superior to window glass, so that it can'be used to advantage in locations'where window glass is clearly unsuitable, and 1n which the cost of plate glass makes it prohibitive. In producing the improved. glass,

relativelyheavy drawn glass, fire finished on ,both sides, is employed, such glass being produced either by a cylinder process, or by a continuous sheet drawing process, such as that of Colburn or Fourcault. This glass is placed upon the ordinary'plate glass grinding table and'ground and polished on one side only, just as heretofore described in con: nectionwith' the surfacing of plate glass, or it may be ground and polished in a continuous straight away process, such as has been recently developed in the art.

- In using the glass, as thus produced, for pictures, the ground. and polished face is placed facing out, so that when viewed at an surface is presented to the observer, and it is difficult to distinguish the glass from plate glass under these conditions. When used for glazing, the glass is also arranged with angle with reflected light, an optically true the ground and polished 'side upon-the ex- I terior, so that the buildingor conveyance in v which the glass is used, has the appearance of being glazed with plate glass, rather than windowgla'ss. Viewed from the inside, also,

the glass presents a much better appearance than ordinary window glass, as the fact that one side is optically true very materially reduces the distortion apparent to an observer when looking through the glass at an angle. When used for mirrors, the ground and polished side will be used facing inward, as it is this side which provides the reflecting sur-' face. The glass may also be used to advantage in making composite wind shields-0f the so-called. splinterless glass. This glass is now made of thin sheets of plate glass Ce, mented to an interposed sheet of celluloid or some other'tough transparent material. In applying the improvement in this relation, the glass sheets have their firepolishedsurfaces 7 next to the celluloid. A composite sheet thus made is much cheaper than one made from glass sheets ground and polished on both sides, and at the same time: is very diflicult ;to. distinguish from such more expensive glass What I claim is: v v

1. As a new article of manufacture, a com; posite sheet'consisting of a pair of opposing plates of drawn glass, each having upon'one side a natural finish, and having the other side ground and polished, andan interposed sheet of tough transparent material, the natural-finished sides of theglass plates facing inward and being attached to said tough transparent sheet.

2. As a new article of manufacture, a composite sheet consisting of a pair of opposing plates of drawn glass, each having upon one side a natural fire finish, and having the other side ground and polished, and an interposed sheetof celluloid, the fire-finished sides of the a glass plates facing inward and being ce-v mented to said celluloid sheet.

3. As a new article of manufacture, a composite sheet consisting of a pair of opposing plates of glass, each having upon one side a natural finish, and having the other side ground and polished, and an interposed sheet of tough, transparent material, the natural finished sides of the glass plates vfacing inward-and being attached to said tough, transparent sheet. i In testimony whereof,-I have hereunto subscribed my name, this 17th day of April,

HENRY B. HIGGINS. 

